The present invention relates to battery handling systems for batteries used in electrically propelled vehicles and, more particularly, to a battery management system for automatically transporting batteries between vehicles and battery charging stations and for checking battery operating characteristics during handling.
Battery powered vehicles such as forklift trucks and automated guided vehicles (AGV), commonly used in factory environments, utilize relatively large batteries for powering the vehicles. A typical battery for a forklift truck may weigh as much as 4,000 pounds and include 24 separate cells. Batteries for AGV's are typically used in pairs with each battery of the pair weighing approximately 800 pounds. In order to achieve efficient operation of such forklift trucks and AGV's, it is common practice to require that the batteries be removed from these vehicles for recharging. In a typical system, an operator would disconnect the batteries from the vehicle and use a separate transport vehicle for removing the batteries from the forklift truck or AGV and transporting the batteries to a battery charger station. The batteries are then connected to the charger and left in the station for a suitable recharge period. The operator then loads another set of batteries determined by FIFO onto the battery transport device and carries those batteries to the vehicle where they are then loaded on to the vehicle and again reconnected to allow the vehicle to be powered from the batteries. One method and apparatus for improving this process is shown in U.S. Pat. No. 4,795,358 which discloses a motion actuated connector apparatus for automatically connecting and disconnecting the batteries from the vehicle and from the charger station. Use of this connector apparatus simplifies the process of transporting batteries by eliminating the need for an operator to manually connect and disconnect battery terminals at the vehicle and at the charger station. However, the system disclosed in this patent does not obviate the need for an operator to manually move the battery between the vehicle and the charger station.
It is also desirable when a battery is charged to check the battery for water level in each cell. In general, the battery manufacturer specifies a particular water level for each cell which will prevent overflow during charging and which will assure that the individual plates within the cell are fully covered by the water-acid liquid within the cell. During the charging operation, if the battery cells are filled to too high a level, the water will tend to boil out of the cell creating an acid spill on top of the battery and on the charger apparatus. It is common practice for the operator to check the water level in the battery by individually opening the caps on the cells and looking inside the battery to determine whether the water is at the proper height. As a matter of practice, it has been found that the cells which are farthest from the operator position in a battery fail first because those cells are not easily inspected without the operator bending over the battery and stretching in order to actually physically check the water in those cells. For example, a typical battery may be 36 inches in length requiring that the operator stretch at least that far from one end in order to check the water level in the extreme end cells of the battery. Furthermore, even though the operator may check the water level in the battery and periodically fill the cells, there is no method for determining whether any cell is overheating and therefore needs to be replaced by simply monitoring the water level in any particular cell. Furthermore, it is not believed that there has been any prior attempt to uniquely identify each battery used in such electric vehicles for the purpose of anticipating any failure of a battery from the battery's charging history.